1. Field of the Invention
The present invention pertains to the capacitive sensors used for the measurement of displacements and, more particularly, for the measurement of very small displacements such as the twist or torsion to which an engine shaft is subjected. These measurements of displacements make it possible to determine the value of the physical magnitude that has caused the displacement: temperature, pressure, force, acceleration etc. Thus, the measurement of the angle of twist of an engine shaft makes it possible to determine the value of the engine torque transmitted by this shaft.
2. Description of the Prior Art
Capacitive sensors such as these are known. Prior art sensors are formed by capacitors with plane, parallel electrodes located at a short distance from each other but fixed in zones that are relatively distant from each other, so that the displacements of these two zones with respect to each other cause variations in capacitance that are sufficient to be used by a measuring electronic system associated with the sensor.
There are difficulties related to the making of these sensors, especially when great measuring precision is sought and when the environmental conditions are difficult, for example when there is a wide range in the working temperatures, a high degree of vibrations etc. For, the making of the measuring capacitors, the plane, parallel electrodes of which should be located at a short distance from each other but should be fixed in two zones that are relatively distant from one and the same structure to be examined, entails machining operations and assembling processes that are difficult and costly. Furthermore, the fastening of the plane electrodes or electrode supports should provide for the electrodes to be completely fixed but should not introduce mechanical stresses liable to deform the electrodes. Now, it proves to be difficult to make a fixed arrangement of this type, because of the differences between the expansion coefficients of the materials to be assembled.